I jumped on the free Win10 upgrade when it was available, now I am at the point where I need to install a new (bigger) OS drive, is there way of doing a clean install of Win10 without having to buy a copy?

And if you want a clean installation regardless, the machine should still be validated with the Windows 10 activation server provided nothing else is changing. Once you log back into your Microsoft Account (if using one) it should be entirely painless. Otherwise, if it doesn't activate for some reason, you might have to click the link under "System Properties" and then do the Robot Phone thing.

1) If all you want is to move from drive to drive, just clone it. Macrium Reflect Free is will do that. Online, too—no need to boot into a mini-OS to clone it.2) If you want a clean reinstall, just go ahead. MS's activation servers will detect your hardware signature and you won't have to do anything.

There is a fixed amount of intelligence on the planet, and the population keeps growing :(

1.) Use something like Magic Jellybean to copy your current Windows 10 license (Just in case) - Windows 10 automatically ties a license key to your hardware, so no need to type it in again.2.) Download Windows Media Creation tool, make sure you have a 4-8gb flash drive to install it on. https://www.microsoft.com/en-us/software-download/windows103.) Swap out your physical drive for the new one.4.) Run the Windows 10 Installer from your created USB media.5.) Plug your old drive back in and move all of your data over to new drive.

This is all assuming you don't want to use something like Macrium or Acronis to image/clone to your new drive. If you so happen to get a Samsung or Crucial, I know those and most SSD come with cloning software. Most all of these automatically handle expanding your drive. So if you go from a 250gb drive to a 500gb, they typically automatically expand your old partition out for you.

"I think there is a world market for maybe five computers." Thomas Watson, chairman of IBM, 1943

What about a bigger upgrade, like replacing the CPU, MOBO and RAM in my gaming system (currently on Ivy Bridge). Is that a situation where I should be able to get Microsoft to let me continue my license? Or do I need to budget $100 for new windows too?